Line bottom of baking pan with parchment paper or grease it with butter.

Place oats, flour, sugar, salt and butter in a bowl and stir until clumps form. Set 1/3 of the crumble mixture and sprinkle the rest of mixture over the prepared baking pan. Press evenly in the bottom of the pan.

Spread the diced fruit over the crust, sprinkle it evenly with cornstrach, lemon juice and sugar.